Cold air can creep into your home through gaps and cracks around doors and windows.
Sealing these gaps keeps the warm air in and the cold air out. You can find the source of a draught by holding an incense stick or candle near doors, windows and other joins. Does the air move the smoke?
How to seal gaps:
Gaps beneath doors can be covered with a rolled up towel or "door snake"
Use tape to seal around the sides of doors and windows
If the gap is uneven, you can use a weather stip. It has a rubber seal (like on your fridge)
For the bottom of outside doors, you can use a weather seal or brush strip. Find out more.